The invention is directed to a lance head in a water-cooled oxygen lance for treating melts, especially for oxygen top-blowing onto steel melts in a converter, with at least one expansion nozzle which widens conically in the direction of the bath surface proceeding from a pipe portion having the narrowest nozzle cross section.
Oxygen lances are used in steel mills operating on the basic oxygen process. In such steel production processes, especially the LD process, as it is called, accompanying elements contained in the crude iron are removed by means of oxygen through oxidation. For this purpose, oxygen is blown onto the melt located in the converter via the-lance at high speeds of MACH 1.0 and greater.
In order for the lance head to operate in the desired manner with respect to the metallurgy of the steelmaking process, the required amount of oxygen must contact the metal melt in an optimum way via the nozzle outlet openings. The individual oxygen lance heads are designed according to specifications oriented to the particular steel mill. In particular, the converter capacity, converter dimensions, actual bath level, and the quantity and pressure of oxygen are taken into account.
DE 37 00 892 A1 discloses an oxygen lance conventionally used in steel mills for treating melts, especially for top-blowing oxygen onto the metal melts, in which is provided a plurality of gas outlet openings diverging relative to the principal axis of the lance and having the narrowest possible critical cross section, as it is called, wherein the critical cross section is adjoined in the direction of flow by a conically widening expansion nozzle.
Lances of this construction can provide only an erratic oxygen jet which disadvantageously results in unwanted steel spray and extensive dust development in the mouth region of the converter.
The object of the present invention is to provide an oxygen lance head of the generic type in which the oxygen jet makes better use of energy, improves the reaction conditions in the converter and reduces the environment burden.
This object is met by the invention through the characterizing features of claim 1. The additional claims show advantageous further developments of the invention.
The above stated object is obtained by a lance head of the invention. An annular chamber which expands in diameter radially outward is provided in this duct which can be guided virtually up to the mouth of the nozzle. As a result of this constructional shape, there is obtained a pulsing gas jet which exits the nozzle so as to be stably structured and impinges on the surface of the melt.
The nozzle is so constructed that speeds in the range of 1 to 3 Mach can be obtained at pressures of up to 15 bar. The oscillation frequency of the gas is adjustable within a range of 200 to 2000 Hz. The preferred frequency range is between 600 and 800 Hz.
As a result of the stable structure of the jet, oxygen quantities can be used with a high degree of energy utilization for blowing on or blowing in a metal melt for steel processing.
Due to the fact that the jet impinges on, the surface of the bath into a steady or smooth manner, the tendency of the molten bath to spray is eliminated and dust generation is reduced.
The stabilization of the gas jet is improved in that the construction of the annular duct is not smooth. For this purpose, the annular chamber is divided into a plurality of chamber segments divided by crosspieces or webs. The chamber segments have different radii, wherein chamber segments located opposite one another by pairs have the same radius.
In another embodiment, the outside walls of the chamber segments have radii which increase continuously in a curved manner.
In a particularly simple construction, disks are arranged in series such that the webs correspond to one another and chamber segments with different radii are arranged in the direction of flow.
The expansion part of the nozzle adjoining the annular chamber in the direction of flow can be partly cylindrical before opening conically in the region of the mouth. The cylindrical portion has a positive influence on the pulsing jet and further stabilizes it especially with respect to rotation in the axial direction.
The region of the critical diameter of the nozzle is rounded corresponding to the shape of a Laval nozzle. Further, in a simple manner as regards manufacturing technique, this region is composed of conical and cylindrical shape elements.
To further influence the desired frequency of the gas jet, one or more steps can be provided between the first conical widening in the inlet region of the nozzle and the annular chamber. The individual steps are offset from one another so as to form sharp edges and stimulate the gas jet to oscillate.
The mouth of the conical widening can have a diameter corresponding to that of the cylindrical duct. A smaller mouth diameter is provided in an advantageous manner, since, in this way, there is already a first step at the entrance to the duct by means of which a positive influence is had on the pulsing of the gas jet.
The various features of novelty which characterize the invention are pointed out with particularity in the claims appended to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.